Evidence recovery from the post impact characterization of a Full Metal Jacket 9 mm Parabellum bullet

Abstract

We demonstrate here how the shooting distance of a 9 mm Parabellum FMJ bullet (115 gr) has been estimated both via shooting experiments and computer simulation. A 9 mm bullet was found by investigators near a concrete wall, fairly distorted at its tip. The bullet carries no evidence of multiple impact and no evidence of ballistic impact on the wall has been reported. We estimated the impact velocity by comparing the questioned bullet with a set of comparison bullets hitting a wall (rigid target) with different velocities. These comparison bullets were obtained both by experimental and numerical means. The estimated velocities (experimental velocity and numerical velocity) exhibit a very good concordance. The shooting distance was recovered from the impact velocity by studying the typical behaviour of a manufactured 9 mm bullet weighting 115 grains (7,45g), shot in pistol or a sub machine gun. The results demonstrated that the questioned bullet was a lost bullet. The shooting distance also helped the investigators, narrowing the range of the estimated positions of the shooter. 1. CONTEXT OT THE STUDY The ballistic department at the Forensic Science Laboratory in Lille was requested to give any helpful information about a gunshot. A firearm bullet, found near a concrete wall in an urban area, has been seized by the investigators. A witness described how he saw a bullet falling down beside his feet after hitting a wall. The bullet is a 9 mm Parabellum FMJ (Full Metal Jacket) bullet weighting 115 gr (7,45 g). It remained complete its jacket unbreached after impact. The observed distortion is fairly small, and limited to the tip of the bullet. The bullet carries no evidence of multiple impact. The tip of the bullet shows evidence of impact against a rough and hard target under normal incidence. No evidence of ballistic impact (scratches or matter ablation) on the wall has been reported. Beside the normal characterization (barrel twist, caliber, type of weapon), investigators questioned us whether it was possible to give the shooting distance. The way to give a shooter's position must classically involve two impacts. The line passing by the center of each impact figure can be materialized with a laser or a set of rods. It can also be calculated from an accurate 3D positioning of each impact. A correction of the bullet's path deflection (under the influence of its weight) can be taken into account in some particular cases. In a gunshot such as the investigated one, only one impact is involved. No information about the position of the shooter can be given. According to our experience, a firearm shot involving 9 mm bullets hitting a concrete wall within a typical combat distance (0-50 m) would leave a fragmented bullet. In this situation, our answer would be that the shooting distance is far beyond 100 meters, and it is likely that the wall was not the target (1). Although this information is quite important, that will not help so much the investigators to find out the shooter's position. The second limitation of the classical way to recover a gunshot trajectory is the lack of knowledge about impact phenomena (deflection, velocity loss, bullet's integrity and stability) which are qualitatively known but not quantified. Their influence can be critical with long range gunshot and/or high incidence impacts.